build: Upgrade Pillow dependency

This upgrade handles multiple high severity vulnerabilities. I've not
checked the affected code in great depth but the APIs we use may be
affected. If they could actually be exploited is another matter which
would take a whole lotta effort which I'd rather not test xD

Fixes: CWE-74, CWE-125, CWE-120, CWE-125, CWE-400
CVE IDs: CVE-2022-22817, CVE-2022-22816, CVE-2021-34552, CVE-2021-23437

requirements.txt

@@ -32,7 +32,7 @@ openpyxl~=3.0.7
 passlib~=1.7.4
 paytmchecksum~=1.7.0
 pdfkit~=0.6.1
-Pillow~=8.2.0
+Pillow~=9.0.0
 premailer~=3.8.0
 psutil~=5.8.0
 psycopg2-binary~=2.9.1